China
Africa
Explore chapters and articles related to this topic
Sustainable Nanotechnology Development Using Risk Assessment and Applying Life Cycle Thinking
Published in Jo Anne Shatkin, Nanotechnology, 2017
Nonstick polymer coatings are frequently used to coat cookware, packaging materials, fabrics, and medical equipment; they reduce friction, increase water resistance, retard flammability, and limit staining potential. As a polymer, these coatings have little to no toxicity when the compounds used to make them are tightly bound in the matrix. But when heated to high temperature, the building blocks of the polymer can release into the air. Some of these building blocks—perfluorinated organic compounds—have been found to be very persistent in the environment. Persistent compounds are of environmental concern because they bioaccumulate; that is, low levels in the environment tend to increase in concentration as they move up the food chain, for example from water to small fish to bigger fish to fish-eating birds and wildlife. Perfluorinated compounds have been measured in people’s blood in countries all over the globe as well as in drinking water, fish, birds, and marine mammals, including polar bears off the coast of Greenland (Bossi et al. 2005; WWF 2004). Some of these compounds (e.g., perfluorooctane sulfonate [PFOS]) are no longer manufactured, and U.S.EPA is conducting a risk assessment of several of the perfluorinated compounds.
Carbon Nanotubes-Polytetrafluoroethylene Nanocomposite Coatings
Published in Vikas Mittal, Polymer Nanocomposite Coatings, 2016
Natthakan Rungraeng, Soojin Jun
SWCNT and MWCNT are cylindrical structures of carbon atoms having single and multiple graphene walls, respectively. The aspect ratio (length (L)/diameter (D)) of these nanotubes are typically higher than 1000. Therefore, they possess a number of exceptional attributes making them suitable for various applications. The synthesis of CNTs done by the CVD process involves the thermal decomposition of hydrocarbon vapor at high temperature in a quartz tube producing carbon and hydrogen species. The isolated carbon atom subsequently reacts with the metal catalyzer on the substrate resulting in initiation and growth of CNTs on the surface of the substrate. PTFE is a low surface-free energy thermoplastic commonly used as a coating material on metal surfaces creating hydrophobic nonstick surfaces, in particular for food-processing equipment. However, the major drawbacks that limit the use of PTFE are low thermal conductivity as well as wear resistance. This reflects the short lifetime of the PTFE coating layer onto the substrate. To overcome this problem, dispersion of CNTs in a PTFE matrix is found to significantly lessen the wear rate of PTFE by several hundred times. Physical blending, in situ polymerization, and chemical functionalization are the main dispersion methods that have been used to efficiently fabricate uniform CNT–PTFE composites. Other than mechanical improvement, properly aligned CNT particles in a matrix also greatly improve the hydrophobic property of CNT–PTFE composites. The presence of CNT particles in a PTFE matrix sufficiently produces a rough surface that accommodates a number of air gaps. This promotes a self-cleaning attribute, the so-called lotus effect, which significantly reduces the amounts of biological foulants on the CNT–PTFE-coated surface. Anti-biofouling performances of CNT–PTFE composite coatings were demonstrated in two distinct situations that are generally associated with food processing, namely (i) milk fouling on the surface of plate heat during pasteurization caused by heat denaturation of natural whey protein and (ii) reduction of bacterial adhesion in liquid flow channel According to the results obtained from both experiments, CNT–PTFE nanocomposite coatings seem to be a promising anti-biofouling technique that substantially reduces the need of tedious process downtime for CIP protocols in the dairy industry during milk pasteurization as well as preventing the risk of cross-contamination of pathogenic bacteria from biofilms formed on the surfaces of food-processing equipments, thus improving food safety in ready-to-eat products.
Composite Fouling Characteristics on Ni-P-PTFE Nanocomposite Surface in Corrugated Plate Heat Exchanger
Published in Heat Transfer Engineering, 2021
Zuodong Liu, Zengchao Chen, Wei Li, Zhikou Ding, Zhiming Xu
Appearances of the uncoated SS-304 plate and the Ni-P-PTFE coated plate are shown in Figure 2a,b, meanwhile the SEM images of the corresponding surfaces is shown in Figure 2c,d. From Figure 2a,b, it can be seen that the coated plate was relatively dark in color while the uncoated SS-304 plate showed a bright silvery appearance. From Figure 2c,d, it was found that the surface of SS-304 plate had ravine-shaped microgrooves on it which may be caused by the manufacturing process, and was very clean without any contaminant, while the surface of Ni-P-PTFE coating was very smooth, on which uniform distribution of PTFE nanoparticles was observed. This kind of micro morphology was consistent with the result revealed by Zhao and Liu [39]. In general, nonstick behavior was regarded to depend on the uniform distribution of PTFE particles on the top surface of the coating. This observation indicated that the electroless composite plating technology was stable and feasible for PHE surface modification.
Bacterial community in a freshwater pond responding to the presence of perfluorooctanoic acid (PFOA)
Published in Environmental Technology, 2020
Dongqing Zhang, Weilan Zhang, Yanna Liang
Perfluorooctanoic acid (PFOA; C8) is a member of the class of perfluoroalkyl and polyfluoroalkyl substances (PFAS), which have attracted increasing concerns over the last decade due to their potential ecotoxicological effects and ubiquitous occurrence in the aquatic environment [5,6]. PFOA has been used as a processing aid in the production of polytetrafluoroethylene (PTFE) and other fluoropolymers, which are often used as non-stick coatings on cookware, membranes for waterproof clothing, electrical wire casing, fire and chemical resistant tubing [7]. PFOA is considered as extremely persistent and is resistant to typical biodegradation processes due to their strong carbon-fluorine bonds [8]. PFOA differs in several ways from other well-studied organic chemicals (e.g. polychlorinated biphenyl and chlordane) that usually have high octanol/water partition coefficients (log Kow), resulting in high affinity to sediments and low water solubility. In contrast, PFOA is highly water-soluble and exists predominantly as an anion under environmental conditions, leading to less binding affinity to soil or sediments [9].
Hydrophilic and hydrophobic materials and their applications
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2018
Darem Ahmad, Inge van den Boogaert, Jeremey Miller, Roy Presswell, Hussam Jouhara
Hydrophobic and SHO can be applied to various types of metal to improve their performance. Polytetrafluoroethylene (TEFLON) is often applied to aluminum alloys to increase the surface hydrophobicity. A very common application of TEFLON is pan coatings. The TEFLON coating is highly hydrophobic (θe ≈ 120°), which results in a non-stick coating which prevents food to stick to the pan (Chou et al. 2010; Derby et al. 2014; Elkhyat et al. 2004; Sarkar, Farzaneh, and Paynter 2008).